Industrial control systems and distributed control systems (DCS) interface with a variety of field (or input) devices. From a control or host device perspective, input devices (e.g. as transducers and sensors) are devices that transmit signals to the control or host device. On the other hand, output devices, such as actuators, coils, and solenoids receive signals from control or host devices. Field devices may transmit or receive signals to and from control devices using two, sometimes three or four wires. They may transmit or receive analog or digital signals in the form of discrete levels, analog signals, or modulated signals, such as frequency shift keyed (FSK) modulated signals. The FSK signals are modulated according to the Highway Addressable Remote Transducer (HART) communication protocol.
In practical applications, large numbers of field devices have a variety of architectures. Historically, to interface with such a large number of disparate field devices, an equally large number of I/O modules was required.